The properties of liquid crystalline (LC)-polymers differ from those of amorphous or crystalline polymers in ways that often have commercial value. Heretofore, the term "mesomorphous" has been synonymous with "liquid crystalline". LC polymers are known to form mesophases having order intermediate between crystalline polymers and amorphous polymers. See Flory, P. J., Advances in Polymer Science, Liquid Crystal Polymers I; Springer-Verlag; New York (1984) Volume 59; Schwarz, J. Mackromol, Chem. Rapid Commun. (1986) 7, 21. Further, mesophases are well known to impart strength, toughness and thermal stability to plastics and fibers as described by Kwolek et al. in Macromolecules (1977) 10, 1390; and by Dobb et al., Advances in Polymer Science, Liquid Crystal Polymers II/III (1986) 255(4), 179. Very recently it has been recognized that polymeric networks made by cross-linking LC polymers and oligomers also have greatly enhanced properties.
Because of their inherent scientific interest and of their many actual and potential commercial applications, LC polymers have been extensively studied. Many published studies have focused on identifying and classifying the kinds of chemical structures that are associated with liquid crystallinity in polymers. These studies have led to formulation of a principle, which has been generally accepted: that liquid crystallinity in polymers is invariably associated with the presence of "mesogenic groups". Mesogenic groups are chemical structures within the polymer which are capable, in certain circumstances, of imparting liquid crystallinity. Lengthy review articles cataloging and classifying mesogenic groups have been written. Most commonly, mesogenic groups are chemical structures that contain a rigid sequence of at least two aromatic rings connected in the para position by a covalent bond or by rigid or semi-rigid chemical linkages. Optionally, one of the rigid aromatic rings may be naphthalenic rings linked at the 1,5- or 2,6- positions. Of several broad classes of mesogenic groups, the most common contains two or more 1,4-arylene (or, less commonly, 1,4-trans-cyclohexenyl) rings covalently connected by rigid or semi-rigid linkages which include but are not limited to ##STR1## and various mesogens described in Ober et al., Liquid Crystal Polymers with Flexible Spacers in the Main Chain, Advances in Polymer Science 59, 104 at 105-117 which is incorporated by reference herein.
Until recently the study of LC polymers as potential coatings binders has received little attention. Chen et al., J. Coat. Technol. 1988, Vol. 60 (756), p. 39 prepared alkyd resins with mesogenic poly p-hydroxybenzoic (PHBA) acid segments (a common LC monomer) pendant to the polymer backbone. Improved dry times and film properties were observed for the alkyds. Chen et al., J. Appl. Polym. Sci. 1988, Vol. 36, p. 141 also prepared LC acrylic polymers with pendant poly PHBA groups that gave excellent lacquer and enamel properties. Wang et al., Polym. Mater. Sci. Eng. 1987, 56, 645, prepared oligoester diols which were end-capped with PHBA units. Cross-linked enamels were prepared that displayed excellent properties. Dimian et al., Polym. Mater. Sci. Eng. 1987, 56, 640, synthesized LC oligomer diols based on the mesogen 4,4'-terephthaloydioxydibenzoyl chloride. The LC diols were cross-linked to give enamels with excellent properties.
Japanese patents have claimed that PHBA enhances the properties of polyester powder coatings; Japanese Kokai 75/40, 629 (1975) to Maruyama et al.; Japanese Kokai 76/56/839 (1976) to Nakamura et al.; Japanese Kokai 76/44,130 (1976) to Nogami et al.; and Japanese Kokai 77/73,929 (1977) to Nogami et al.
In classifying "mesogenic groups" one also, overtly or by implication, classifies other groups as "non-mesogenic". Such groups are chemical structures that are outside the boundaries of the various types of mesogenic groups. They are generally considered incapable of imparting liquid crystallinity under any circumstances. Two types of non-mesogenic groups are of particular interest: (1) single 1,4-arylene units that are connected to other aromatic rings in the polymer structure by flexible rather than rigid or semi-rigid linkages and (2) 1,3-arylene rings connected in any way. Examples type of (1) and groups derived from terephthalic acid, hydroquinone and 4-hydroxybenzoic acid are: ##STR2## Examples of non-mesogenic groups of type (2) are those derived from isophthalic acid, resorcinol and 3-hydroxybenzoic acid: ##STR3##
In a recent publication [Kricheldor, Pakull and Buchner, Macromolecules, 21, 1929-1935 (1988)] it was reported that a polymer containing two electronically different aromatic non-mesogenic groups is "liquid crystalline". The structure of this polymer is: ##STR4## Krichedor et al. considered their finding very surprising. They explained the formation of liquid crystallinity by postulating a "special co-operative effect, presumably a charge-transfer interaction, between the aromatic monomer units." They stated " . . . the mesophase of 4e (the above Formula 1) is formed despite the absence of mesogenic groups. Obviously, special interaction between the bisphenol and the benzophenone imide unit is responsible for the observed smectic phases. This interaction is most likely a weak charge-transfer (CT) complexation." It was taken as a given that the isolated bisphenol unit is not a mesogenic group which may be a matter of semantics when the resulting compound exhibits LC-like properties. Indeed, semantically because the resulting compounds have LC-like properties certain linkages or parts of the compounds may be considered mesogens or mesogenic.
In another publication [Bilibin, et al. Makromol. Chem., Rapid Commun. 6, 209-213 (1985)] it was reported that chemical compounds of the structure ##STR5## " . . . exhibit monotropic mesomorphism. This can be accounted for by intermolecular hydrogen bonding as in the case of the 4-alkoxybenzoic acid melt." Also see Fornasier et al. Liquid Crystals 8, 787-796 (1990).
It is an object of this invention to provide polymeric vehicles for coatings binders which have LC-like properties.
It is another object of this invention to provide a method of imparting LC-like properties to coatings binders.
It is still another object of this invention to provide solvent dispersible polymeric vehicles for coatings binders which have LC-like properties.
It is yet another object of the invention to provide a method which provides polymeric vehicles with new thixotropic and anti-sagging properties.
Still further objects and advantages of the invention will be found by reference to the following description.